I keep mulling the concept "chimeric embryo" now that I've read Bill Heinze's postthat the U.S. Patent and Trademark Office is examining what it means to be human. Apparently the USPTO is waiting on a National Academy of Sciences report due in April. Heinze writes:

"I don't think anyone knows in terms of crude percentages how to differentiate between humans and nonhumans," John Doll, Deputy Commissioner for Patents at the USPTO, reportedly told The Washington Post. Yet neither is the office comfortable with a "we'll know it when we see it" approach, he added: "It would be very helpful ... to have some guidance from Congress or the courts."